Biodiesel is an environmentally benign solution for global warming, the energy crisis and depleted fossil fuel supplies. Today, biodiesel (e.g., fatty acid methyl esters, “FAMEs”), is the name given to clean burning alternative fuels, produced from biological, renewable resources that are biodegradable and non-toxic. Biodiesel can be used directly or can be blended at any level with petroleum products, such as petroleum diesel.
Biofuels have clear benefits in addressing environmental concerns related to greenhouse gases, and offer new income to farmers. However, traditional oil-rich crops are limited by land availability, as well as environmental and social issues regarding the use of feed and food crops for fuel. An alternative way to produce biodiesel in a green and sustainable manner without competing with food crops is to use microbes. There are a few microorganisms in nature that have the inherent ability to accumulate or store oil/lipid up to 60% of their dry weight when grown under nitrogen-limited conditions. These lipids usually consist of 80%-90% triacylglycerols with a fatty acid composition similar to many plant seed oils (Ratledge, C., Evans, C. T. (1984) Influence of nitrogen metabolism on lipid accumulation in oleaginous yeasts. J. Gen. Microbiol. 130:1693-704.
Ykema A, Verbree E C, Kater M M, Smit H (1988) Optimization of lipid production in the oleaginous yeast Apiotrichum curvatum in whey permeate. Appl Microbiol Biotechnol 29:211-218). These organisms are called oleaginous microorganisms. Microbial oils, also called single cell oils, are produced by some oleaginous microorganisms, such as yeast, fungi, bacteria and microalgae (Ma, Y. L. (2006) Microbial oils and its research advance. Chin. J. Bioprocess. Eng. 4(4):7-11.). It has been demonstrated that such microbial oils can be used as feedstock for biodiesel production. In comparison to other vegetable oils and animal fats, the production of microbial oil has many advantages: microbes have a short life cycle as compared to plants so the time to harvest is shorter, there is less labor required, microbial oil production is less affected by venue, season and climate, and scale-up is easier (Li, Q., Wang, M. Y. (1997) Use food industry waste to produce microbial oil. Science and Technology of Food Industry 6:65-69.). Therefore, microbial oil has a tremendous potential to become one of the major oil feedstocks for biodiesel production in the future. Although not a new concept, work in this area has been very limited (Li, Qiang., Wei, Du., Dehua, Liu. (2008) Perspectives of microbial oils for biodiesel production. Appl. Microbiol. Biotechnol. 80:749-756.).
Microbial cells studied to date for use in biodiesel production include bacteria, yeast and fungi. Preferred fungus genera include Mortierella, Phycomyces, Entomophthora, Pythium, Thraustochytrium, Blakeslea, Rhizomucor and Aspergillus. Exemplary bacteria that have been studied include those of the genus Propionibacterium. Studied algae include dinoflagellate and/or belong to the genus Crypthecodinium, Porphyridium or Nitschia, for example Crypthecodinium cohnii. 
Yeasts such as Yarrowia, Candida, Rhodotorula, Rhodosporidium, Cryptococcus, Trichosporon and Lipomyces have been studied for their microbial oil properties and among these oleaginous yeasts, Cryptococcus curvatus has attracted attention because it can accumulate large amounts of oil, up to 60% of the cell's dry weight (Ratledge, C. (1991). Microorganisms for lipids. Acta. Biotechnol. 11:429-438), utilizing cheap carbon sources like whey permeate (Ykema, A. (1989) Lipid production in the oleaginous yeast Apiotrichum curvatum. PhD thesis. Free University Amsterdam, The Netherlands.) and other carbohydrate-rich agricultural or food processing wastes. The yeast oil produced by C. curvatus resembles plant seed oils like palm oil (Davies, R. J. (1988) Yeast oil from cheese whey; process development. In: Moreton R S (ed) Single cell oil. Longman, London, pp 99-145.). Yeasts of the genus Pichia and Saccharomyces, for example Pichia ciferrii, have also been studied.
Currently, the production of yeast oil is more expensive than the production of vegetable oil. Therefore, single-cell oil fermentation will be economically feasible when a particular oil can be produced with high added value. Accordingly, previous approaches have used process engineering to yield a higher lipid production rate, a higher cellular lipid content, and higher biomass production, all geared to make the process more economically feasible. Different cultivation modes, including fed-batch and continuous fermentations, have been reported to increase the cell density of oleaginous microbes in culture. However, none of the prior art focuses on the efficient extraction of oil from fermentation media.